Electrical motors are in wide-spread use and can be found in every aspect of industrial, commercial and residential life. Motors can vary from small, fractional motors that are found, for example, in washing machines, refrigerators and air conditioners, to large industrial applications for driving manufacturing equipment, compressors, fans and the like. Motors are used to convert electrical energy into rotating energy or rotational force.
A typical motor includes a rotating central portion known as a rotor and a stationary outer portion referred to as a stator. Both the stator and rotor are housed in a housing that carries the motor. The rotor and stator contain electrical conducting elements through which the electrical energy is converted to rotational energy. Rotor and stator cores can be formed with varying numbers of slots which are the openings that receive the electrical conducting elements.
The stator core is that portion of the motor that contains stationary conductive elements. The number of slots in stator cores can vary considerably. In smaller, fractional squirrel-cage motors, for example, those having diameters of about two inches, the number of slots is generally between 8 and 52. The stator core structure is typically formed from a plurality of stacked plates or laminations. The laminations which are generally formed from metal, may be punched or pressed and subsequently stacked one on top of another to form the stator core. Due to the possible asymmetries in the lamination material, the laminations can be rotated so that the stator core, upon final assembly, forms a straight rather than lopsided stack The laminations are interlocked with one another to form a rigid stator core structure and to prevent the laminations from shifting relative to one another.
In one known interlocking arrangement, each lamination has a dimple or a recess punched into the surface which forms a corresponding projection on the opposite side of the lamination. The laminations are then stacked one on top of the other with the projections from one lamination engaging and residing within the recess in the next adjacent lamination. In this nested arrangement, the laminations are kept in alignment with one another by engagement of the projections and recesses. This is a common and accepted method for interlocking laminations.
Although such known methods are in common practice, they do have their drawbacks. First, there is a mathematical dependency between the number of slots in the stator and the number of interlocks. Specifically, the number of slots and the number of interlocks are chosen such that they are both divisible by 3, 4 or 5 to yield rotations of 120.degree., 90.degree., and 72.5.degree., respectively. Although this may be adequate when the stator has a number of slots that is readily divisible by such numbers, it is unacceptable when the number of slots in the stator varies from these readily divisible numbers. Additionally, when the stator core is formed having an outer shape other than round, that is when the core is formed with "flats" on the outer periphery of the core, the rotation angle must also of necessity be dependent upon the number of "flats" or the corresponding angle between "flats". For example, when the number of slots is 12, 15, 16, 20, 24, 28, 30, 32, 36, 40, 42, 45 or 48, the number of interlocks can be sufficient (e.g., between 3 and 4), and the rotational angles are readily determined by dividing the number of interlocks into 360.degree., so long as the number of flats is readily divisible into the number of slots.
For example, a stator having 12, 24 or 36 slots can include 2, 3, 4 or 6 interlocks which will have rotational angles of 180.degree., 120.degree., 90.degree. and 60.degree., respectively. However, if the stator has 6 flats, this relationship no longer applies, because, for example, the 4 interlock configuration will require at least a 180.degree. rotational angle. Likewise, with 2 interlocks, a 180.degree. rotational angle is required. If the number of flats on the stator is 4, the number of interlocks is then limited to 2 and the rotational angle is again limited to 180.degree.. It will thus be apparent that when the number of slots varies from these readily divisible numbers, and when the number of flats is not a like multiple of the number of interlocks, the incorporation of interlocks into a rotated stator core can become quite complex if not impossible.
It has also been observed that stator cores having laminations that have a number of slots that can only be rotated 180.degree. can be susceptible to forming a lopsided stack or core. Additionally, such cores that include laminations that are rotated only 180.degree. can produce undesirable ovality in the finished core if an offset exists, for example, in punched holes that are intended to be concentric with one another.
Accordingly, there continues to be a need for a stator core lamination interlocking arrangement that is independent of the number of slots and which is dependent only upon the number of flats. Such a configuration desirably accommodates lamination rotations.